Earth Planets Space, Vol. 60 (No. 11), pp. 1131-1135, 2008LETTER
Shin Aoi1, Haruko Sekiguchi2, Nobuyuki Morikawa1, and Takashi Kunugi1
1National Research Institute for Earth Science and Disaster Prevention, 3-1 Tennodai, Tsukuba, Ibaraki 305-0006, Japan
2National Institute of Advanced Industrial Science and Technology, Site 7, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan
(Received December 8, 2007; Revised February 18, 2008; Accepted February 26, 2008; Online published November 18, 2008)
The 2007 Niigata-ken Chuetsu-oki earthquake generated strong ground motions in Kashiwazaki and Kariwa, where the world largest nuclear power plant was in operation. Due to the complexity of the aftershock distribution, activation of the northwest-dipping fault and/or the southeast-dipping fault is proposed. To explore the fault geometry and source process of the earthquake, we performed multi-time window linear waveform inversions for both the fault planes from near-fault strong motion data. A fault plane model of 30 km in length by 24 km in width was set to cover the region of aftershock distribution within 24 h of the mainshock. Both inverted slip models provided moment magnitudes of 6.7 with a small asperity near the rupture starting point, and a large asperity approximately 10 km southwest of the rupture initiation, which is located in the region of relatively sparse aftershock distribution. Both the small and large asperities are located near the intersection between the two conjugate fault plane models, and the asperities of both models have similar radiation patterns. Therefore, the difference of the residuals between the observed and synthetic waveforms for both models was not significant, indicating that it is difficult to conclude which fault is the rupture.
Key words: Source process, waveform inversion, 2007 Niigata-ken Chuetsu-oki earthquake, near-fault strong motion.